1. Field of the Invention
The present invention relates to a throttle grip apparatus for controlling an engine of a vehicle according to a rotation angle of a throttle grip.
2. Background Art
Recently, there has been spread a motorcycle of a type that, a rotation angle of a throttle grip is detected using a throttle opening angle sensor such as a potentiometer and the thus detected value of the rotation angle is sent as an electric signal to an electronic control unit or the like incorporated in the motorcycle. The electronic control unit carries out a given operation according to such detection signal, and an ignition timing of the engine or an opening/closing of an exhaust valve can be controlled according to results of such operation.
For example, in the patent reference 1 (JP-A-04-254278), there is disclosed a throttle grip apparatus having the above-mentioned structure. Such throttle grip apparatus includes mainly a drive pulley portion rotatable in linking with a throttle grip, a detecting gear meshingly engageable with a gear formed in a portion of the drive pulley portion, a potentiometer for detecting a rotation angle of the detecting gear, and a case for storing these composing elements therein. In operation, when a driver rotates the throttle grip, the potentiometer is rotated through the drive pulley portion to thereby detect an opening angle of the throttle grip.
In the above-cited throttle grip apparatus, since the rotation angle of the throttle grip is detected using a throttle opening angle sensor, there is eliminated a need for use of a general-purpose operation cable which transmits a rotation movement of the throttle grip to an engine side. However, this structure also eliminates a sliding resistance that is conventionally generated by the sliding movement of an inner tube relative to an outer tube forming the general-purpose operation cable when the throttle grip is rotated. Therefore, as a force to be transmitted to the driver side when the throttle grip is rotated, there can be provided only a force of a return spring that returns the throttle grip to its initial position, which causes the driver to feel uncomfortable.
In order to solve the above inconvenience, for example, as disclosed in the patent reference 2 (JP-A-2003-252274), there is proposed a throttle grip apparatus structured such that a frictional plate, when the throttle grip is rotated, for applying a frictional force going in the opposite direction to a rotation direction of the throttle grip is disposed in a case fixed at a position adjacent to the throttle grip, and a frictional force generated by the frictional plate is used to produce a rotation load of the throttle grip. According to such prior-art throttle grip apparatus, the use of a throttle wire can be eliminated and also a driver is allowed to operate the throttle grip without feeling uncomfortable.
However, in the conventional throttle grip apparatus including the above frictional plate, since the friction plate is disposed in the case fixed at the position adjacent to the throttle grip, although the rotation load of the throttle grip can be obtained when the throttle grip is rotated, there is raised a problem that the throttle grip apparatus itself increases in size.    [Patent Reference 1] JP-A-04-254278    [Patent Reference 2] JP-A-2003-252274